1. Field of the Invention
The present invention relates to an arbitrary waveform generator for generating a desired waveform and a testing apparatus including the arbitrary waveform generator. More particularly, the present invention relates to an arbitrary waveform generator for generating a waveform with small noises.
2. Related Art
When testing a device under test, a method for inputting a test signal having a desired waveform into the device under test has been conventionally known. For example, the good or bad of the device under test can be decided by comparing an output signal from the device under test when inputting this test signal with an expectation signal.
Conventionally, an arbitrary waveform generator has been used in order to generate a test signal with a desired waveform. This arbitrary waveform generator converts digital data showing a pattern of a waveform to be generated into an analog signal by means of a digital-analog converter (hereinafter, referred to as a DAC). Moreover, a high-frequency component of this analog signal is removed and thus a waveform of this analog signal is smoothened by means of a smoothing filter.
However, in the case of using a smoothing filter, a waveform of an analog signal is distorted if a band of this smoothing filter is narrow. For example, a test of an analog-digital converter (hereinafter, referred to as an ADC) requires a lamp wave having highly precise linearity. However, it is difficult that a lamp wave passing a smoothing filter guarantees linearity because a waveform of the lamp wave is distorted at a starting point and an end point of an edge of the wave.
Moreover, in the case of using a filter in order to remove noises from a test signal, the test signal may be similarly distorted. Moreover, when generating a high-frequency test signal, since an inclination of a test signal becomes steep, it is necessary to broaden bandwidth of a test circuit. When a band of a test circuit is not enough, a test signal is distorted. However, when broadening bandwidth of a test circuit, noises overlapped on a test signal increases. In this manner, in a conventional apparatus, it was difficult to generate a high-speed and low-noise test signal.